The field to which this invention pertains is the separation of fatty acid esters by degree of unsaturation. More specifically the invention relates to a continuous process for separating esters of more unsaturated fatty acids from esters of less unsaturated fatty acids in a mixture comprising the two types of esters, by contacting said mixture with a solid zeolite adsorbent which has a higher affinity for more unsaturated fatty acid esters, and then desorbing the adsorbed esters from the adsorbent.
It is often important to separate fatty materials such as fatty acid esters into fractions of different degrees of unsaturation since there are specific uses for fatty materials having, respectively, higher or lower degrees of unsaturation. This is especially true in the manufacture of drying oils for coatings, the manufacture of resins and plasticizers, the compounding of cosmetic products and in the manufacture of chemical derivatives. For such purposes, a fatty acid ester product becomes more valuable as the proportion of the desired (i.e., more unsaturated or less unsaturated components) is increased in the product.
The zeolites used as the adsorbents herein have a preferential affinity for the more unsaturated components of a fatty acid ester mixture, i.e., the higher the degree of unsaturation, the higher the affinity. Accordingly, in the process of the invention, the fraction of the fatty acid ester feedstock which is adosrbed on the zeolite becomes enriched in the more unsaturated components, while the fraction which remains unadsorbed becomes enriched in the less unsaturated components.
The use of zeolite adsorbents (also called molecular sieves) to separate olefinic hydrocarbons from paraffinic hydrocarbons is well known. For example, U.S. Pat. No. 3,265,750 issued Aug. 9, 1966, to Peck et al., and 3,510,423, issued May 5, 1970, to Neuzil et al., describe the use of X and Y zeolites to conduct such separations.